In general, surgery and surgical treatment involve one or both of tissue separation and tissue joining. In surgery, medical treatment, and medical research, it is desirable to retract tissue, stabilize tissue, and present tissue in a variety of specific orientations to provide access to the area under investigation or repair, ideally in a method that creates minimal trauma beyond what is necessary for exposure and visualization of the operative area. In other words, it is desirable to exert a force on a tissue structure by reference either to some or all of the other tissue of which it is to become a part, as in the case of a transplant. Such an exertion of force for the purpose of tissue manipulation may be accomplished through very simple and short series of elements or through complex and lengthy series of elements that may or may not include gravity as a significant element. Examples of simple series in which gravity is not a significant element include sutures and staples (tissue joining) and a rib spreader (tissue separation).
Moving tissue presents unique challenges, as tissues often resist joining, or closure, depending on the nature of the tissue structure, the circumstances of the tissue separation, and general patient health. Complications related to wound closure and healing generally result from major forces, minor forces and/or compromised healing responses. Major forces are retractive forces created beyond the viscoelastic properties of the tissue, and may be created by: (1) increased internal volume, such as in the case of obesity, which elevates containment forces on the skin system; (2) changes in aspect ratio, such as increased abdominal circumference created in a prone, non-ambulatory patients due to muscular atrophy; (3) respiratory muscular activity; (4) muscular response; (5) loss of fascia structure; (6) muscular-skeletal deformation; (7) fleshy appendages; (8) tumors; and (9) severe burns.
Minor forces are internal forces created by the viscoelastic properties of the tissue, which can cause the skin to retract. Elastic tissues, such as skin, return to a minimum elastic, or relaxed, state when released from tension. In this relaxed state, tissue cells have a spherical shape, cell walls are thick and strong, and cell surface tensions are minimized and balanced. A cell in this minimum elastic state will remain relaxed, demonstrating behavior similar to a non-elastic material. The force required to elongate a cell in this state often approaches a force that will rupture or sheer intercellular bonds, causing localized failures or tears. Soft tissue in this minimum elastic state provides minimum surface coverage and has the highest reluctance to stretch. It is believed that a gentle but constant force below the sheer force threshold applied to tissue in combination with adequate hydration will, over time, restore certain tissues to original elastic state. Additionally, this force can be applied to stretch tissue past the point of equilibrium (normal elastic range) to the maximum elastic range and create the thinnest possible configuration, covering the maximum surface area. If intercellular pressures in the tissue do not exceed the point at which intercellular bonds are compromised, the tissue remains at the maximum elastic state as healthy tissue, and normal biological processes will build additional cells to restore normal skin thickness and tension, which is described below as biological creep.
Plastic tissues, such as skin and muscle, possess certain viscous and elastic rheological properties, and are therefore viscoelastic. Certain plastic tissues are able to increase surface area over time, which can be termed “creep.” “Mechanical creep” is the elongation of skin with a constant load over time, while “biological creep” refers to the generation of new tissue due to a chronic stretching force. A constant and unrelenting force applied to a body tissue, such as skin or muscle, may result in both mechanical and biological creep. Mechanical creep restores the tension originally present but lost in the skin across the incision or wound by retensioning skin or soft tissue cells, thereby increasing skin coverage. Biological creep occurs more slowly and involves the creation of new tissue. Tissue expansion has long been part of the art of plastic surgery, traditionally accomplished with balloon-type tissue expanders embedded under the skin and externally inflated and increased over time to create expanded pockets of skin for procedures such as breast reconstruction after radical mastectomies, and stretching healthy tissue prior to plastic surgery for the creation of flaps for soft tissue closure.
Finally, compromised healing responses may complicate wound closure or healing. A surgical or other incision becomes a wound as soon as it falls behind normal healing protocol. Wound management, including treatment and care of large skin defects and severely retracted incisions, is an area of increasing importance to the health care community. An aging population and an increase in diseases related to obesity and inactivity have increased the occurrence of chronic wounds and place an increased burden on health care resources. Factors contributing to compromised wound healing include patient age, weight, nutritional status, dehydration, blood supply to the wound site, immune response, allergies to closure materials, chronic disease, debilitating injuries, localized or systemic infection, diabetes, and the use of immunosuppressive, corticosteroid or antineoplastic drugs, hormones, or radiation therapy. Chronic wounds include, but are not limited to: diabetic ulcers and other chronic ulcers; venous stastis ulcers; pressure sores or ulcers; burns; post traumatic lesions, such as post disarticulation, post debridement, cutaneous gangrene, post colectomy, crush wounds with ischemic necrosis; collagen disease, including rheumatoid arthritis; vasculitis (lesions and ulcers caused by arterial insufficiency); amputation; fasciotomy; post surgical dehiscence; post stemotomy; necrotising fasciitis; trauma; wounds having exposed plates or bones; scar revision; skin lesions; blunt abdominal trauma with perforations; pancreatitis; neuropathic ulcers; compartment syndrome; and other subacute or chronic wounds. Treatment and care of these defects is challenging due to difficulties in closure of open wounds.
Two common methods of closure of wounds and skin defects include split thickness skin grafting and gradual closure. A split thickness skin graft involves removing a partial layer of skin from a donor site, usually an upper leg or thigh, and leaving the dermis at the donor site to re-epithelialize. In this manner, a viable skin repair patch can be transferred or grafted to cover a wound area. The graft is often meshed, (which involves cutting the skin in a series of rows of offset longitudinal interdigitating cuts) allowing the graft to stretch to cover two or three times greater an area as well as provide wound drainage while healing. Normal biological function of the skin heals the holes after the graft has been accepted. A meshed graft of this type requires a smaller donor area than a conventional non-meshed or full thickness skin graft. However, these methods do not provide optimal cosmesis or quality of skin cover. Other disadvantages of this method include pain at the donor site, creation of an additional disfiguring wound, and complications associated with incomplete “take” of the graft. In addition, skin grafting often requires immobilization of the limb, which increases the likelihood of contractures. The additional operation and prolongation of hospital stay is an additional economic burden.
Gradual, or progressive, closure is a second method of closure. This technique may involve suturing vessel loops to the wound edge and drawing them together with large sutures in a fashion similar to lacing a shoe. In addition, the wound edges may be progressively approximated with suture or sterile paper tape. The advantages of this gradual, or progressive, technique are numerous: no donor site is required for harvest of a graft, limb mobility is maintained, and superior cosmetic result, more durable skin coverage, better protection from full skin thickness and the maintenance of normal skin sensation may all be achieved.
Existing devices for effecting a gradual closure have many disadvantages. Current methods and devices draw wound edges together using mechanical devices such as screw-actuated devices that require repeated periodic adjustment because a relatively small skin movement substantially eliminates much of the closure force. Widely used existing closure techniques involve use of relatively inelastic materials, such as sutures or surgical tape. Excessive tension may cut the skin or cause necrosis due to point loading of the tissue. Current solutions include suture bolsters, suture bridges, use of staples as anchors at the wound edge, and the use of ligature wire to distribute the load along the wound margins. These approaches all rely on static ribbon or suture material, which must repeatedly be readjusted in order to function effectively, and even with this constant readjustment, maintenance of near constant tension over time is difficult, if not impossible, to achieve. Widely used traditional gradual closure methods rely on static force through fixed distance reduction, and do not provide continuous or dynamic tension.
Many current methods of open wound reduction employ static or non-yielding devices such as sutures or hard approximators, which reduce the distance between the wound margins and rely on the skin's natural elasticity to compensate for movement. One problem with these devices has been that when they are at the point of being most effective, when the skin is at the point of maximum stretch, additional skin tension created through motion, such as breathing or walking, creates stress points where the mechanical fasteners meet the wound margins, causing tearing and wound edge necrosis. This has generally required patients to remain immobile during the course of treatment. Existing systems for treating animals need not consider cosmetic result to such a degree as the healthy patient typically masks the wound site with fur, but cosmesis is a critical criteria in the measurement of a successful result from the system in the human application.
One existing method for effecting closure of a wound utilizes a constant tension, low-grade force to draw wound edges together. One device for practicing this method includes a pair of hooks carried by a pair of sliders that move along a path pulled by a pair of springs. This spring device is enclosed in a plastic housing and is available having various curvatures. The sharp hooks used in this system may damage the skin. The constant force used is a dictated force that is not variable. Other closure devices use elastomeric material, including rubber bands and other types of compressive and non-compressive materials, to approximate wound margins. One kit requires bonding to the skin with an adhesive and also requires periodic adjustment to tighten the straps. Other known closure devices use hooks and elastic loops, which must be replaced with smaller elastic loops to maintain tension, or a motor power source to provide a tightening means. Finally, another current device consists of two surgical needles, two U-shaped lexan polycarbonate arms with hooks on the bottom surface, a threaded tension bar and a polycarbonate ruler. The needles are threaded along the wound margin and each arm is positioned above a needle, with the hooks piercing the skin and engaging the needles. The tension bar is then locked, and tension can be adjusted using the screw.
Existing methods of gradual wound closure fail to provide an effective gradual closure that restores original skin tensions lost across the wound. For example, one system has a single tension of 460 grams. In many instances, such as with the elderly or with compromised skin, this force is too great, resulting in localized failures, tears and necrosis. Many current devices are cumbersome, restrict patient mobility, must be completely removed for wound dressing and cleaning, and are usable in a relatively limited number of situations because of size constraints. Many also require a surgeon for reinstallation after removal for wound dressing. Finally, many current devices cannot readily be used for radial closure of wounds due to their limited ability to pull in a single direction along an overhead beam, thereby restricting their application to parallel pulls along the same axis.